The present invention relates to servomotor operated rotary valves and particularly valves of the type intended for on-board motor vehicle application such, as for example, valves employed for diverting flow of air as between plural passages in an engine inlet manifold.
Currently some automotive engines employ different length passages in the inlet manifold for producing different flow characteristics in different regimes of the engine speed/load envelope and a motorized diverter valve is employed for switching air flow from one set of passages to another as the flow requirements of the engine are increased with increasing load and/or speed. The motorized diverter valve for such an application must, of necessity, be small in volume and have a minimal current draw, yet provide fast response in order that the diverter valve can adequately respond to operator throttle input demands. In a typical passenger car or light truck application the engine electronic computer for generating an electrical control signal to drive the diverter valve motor.
Furthermore, it is required to have a high degree of accuracy in positioning the valve during rotation in order to achieve the desired precise amount of flow diversion for engine inlet air in order that the engine operation may be optimized without adversely effecting the combustion and resultant emissions. The electronic engine computer also controls the electrically operated fuel injectors with an algorithm which includes throttle position as an input.
Thus, it has been desired to have a small low current motor for an engine manifold diverter valve capable of operating on a typical low voltage direct current vehicle power supply and which can provide desired accuracy of valve positioning, quick response and sufficient torque to move the valve readily to the desired operating position. Heretofore, this has been achieved by using a gear reduction train with a numerically high overall ratio of a motor input shaft rotation to output valve shaft rotation.
However, it has also been a requirement that such a rotary diverter valve for engine air inlet manifold applications have a provision for return to an initial rotational position in the event of servomotor failure or loss of electrical power once the valve has been rotated from the initial position to an operational air diverting position. However, where a high numerical ratio of speed reduction has been provided between the motor input shaft and the valve shaft, it has been found virtually impossible to provide a spring return for the valve inasmuch as the return spring must have adequate stored energy from winding to back drive the motor shaft through the mechanical disadvantage of the gear train when driven by applying the spring torque to the valve shaft.
Thus, it has long been desired to provide a way or means of spring returning a motor driven rotary diverter valve drivers by a small low current having a high numerical gear reduction in a manner which does not require a heavy return spring resulting in additional drive motor loading in order to overcome the torque of the return spring.
The motorized diverter valve for such engine applications must also be reliable and relatively low in manufacturing cost so as not to render the desired engine control prohibitively costly for high-volume, mass-produced vehicle engines.